Research ArticleChemistry

A deep UV trigger for ground-state ring-opening dynamics of 1,3-cyclohexadiene

See allHide authors and affiliations

Science Advances  06 Sep 2019:
Vol. 5, no. 9, eaax6625
DOI: 10.1126/sciadv.aax6625
  • Fig. 1 UV absorption spectrum of CHD.

    The broad band between 220 and 280 nm reflects the absorption to the 1B state. The sharper peaks at short wavelengths are due to the 3p Rydberg states. A red arrow indicates the 200-nm excitation wavelength used in the present experiment. The inset shows the corresponding time-resolved photoelectron spectrum for the short-lived 3p state.

  • Fig. 2 The anisotropic components of the pump-probe scattering patterns.

    Top: Computed patterns for alignments of the transition dipole moments along the x, y, and z directions. Bottom left: Experimental pattern at 1 ns. Bottom center: Simulated pattern with the optimal admixture of transition dipole moments.

  • Fig. 3 The isotropic component of the time-dependent experimental percent difference scattering signal of CHD as a function of time.

    Plotted on top is the percent difference in scattering intensity (color bar) induced by the laser pulse as a function of the absolute value of the scattering vector, q, and the pump-probe time delay. The bottom panel shows averages over two q ranges (dots) and the kinetic fit as described in the text (lines). Because of the large range of experimental delay times the panels are divided into three time segments: one from −1 to 1 ps to show the ultrafast temporal response to the pump laser pulse; the times from 1ps to 15 ps showing the initial ground-state population; and the time range from 15 ps to 1 ns (on a log scale) giving the increase in HT population as the molecules equilibrate on the ground state potential energy surface.

  • Fig. 4 Reaction Pathway of Rydberg-Excited CHD.

  • Fig. 5 Percent difference scattering signal, scaled for 100% excitation probability, for the hot (6.20 eV) molecules relative to the cold CHD (room temperature) molecules.

    (Top) The experimental scattering signal, represented by black dots with error bars (given in 1σ), and the theoretical patterns to the three conformers, given in blue, orange, and green. A fit to a mixture of the three theoretical signals (20% cZt, 80% tZt) is given as a black line. (Bottom) The separate residuals of the experimental percent difference scattering signals with respect to each of the HT theoretical patterns and the optimal admixture.

  • Fig. 6 Relative populations of the three components of the photoreaction (Eq. 2) on a logarithmic timescale: Electronically excited CHD*, the hot ground-state CHDhot, and the hot ground-state HThot.

    The background colors indicate the different time regimes of the kinetics: Blue is dominated by the decay of CHD*, orange is dominated by the hot CHD, and green indicates the equilibration to 67% HThot and 33% CHDhot.

  • Fig. 7 The potential energy surfaces of CHD allow for reversion to the ground state of the reactant molecule, favored when the wavepacket is close to the plane of symmetry, or ring opening to the HT product molecule, favored when the wavepacket is off symmetry.

    The path through the 2A/1B CIs can either deflect the wavepacket away from the symmetry plane (1B excitation, leading preferentially to the HT product) or focus it onto the symmetry plane (3px,y excitation, leading preferentially to the hot CHD).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/9/eaax6625/DC1

    Section S1. Anisotropic and isotropic scattering decomposition

    Section S2. Kinetics fit

    Section S3. Separating HT rotamers

    Fig. S1. The time-resolved anisotropic scattering signal for CHD excited at 200 nm.

    Fig. S2. The residuals of the kinetics fit, divided into temporal regions as shown in Fig. 3 of the main text.

    Table S1. Criteria for fitting the HT rotamers.

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Anisotropic and isotropic scattering decomposition
    • Section S2. Kinetics fit
    • Section S3. Separating HT rotamers
    • Fig. S1. The time-resolved anisotropic scattering signal for CHD excited at 200 nm.
    • Fig. S2. The residuals of the kinetics fit, divided into temporal regions as shown in Fig. 3 of the main text.
    • Table S1. Criteria for fitting the HT rotamers.

    Download PDF

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article